This invention is directed to problems associated with railway wheel sensors and applications therefor. In particular, the invention relates to means for sensing the passage of railway rolling stock past a specified portion of the track where responsively coupled wayside equipment is normally located. For example, in modern lubricating systems, lubricant such as grease is dispensed onto the track or the flange wheels of the railway rolling stock to assure that wear on the curved sections of track is minimized. The technique requires that the proper amount of lubricant be dispensed and this varies with the length of the train and the consequent number of wheels involved.
Hot box detectors sense overheated journal boxes on passing trains and, using wheel count as a guide, defective equipment is located for repair at a later time. Here accurate wheel count is essential to locating the faulty journal box.
Train detectors for producing a warning signal at a grade crossing also rely on accurate, false alarm free train detection systems. In such applications accurate and unambiguous detecting means is an important feature.
Various transducers have conventionally been employed to sense or detect the number of wheels on moving trains. Examples include simple pressure sensitive switches tripped by the flange wheels of a passing train and more sophisticated electronic devices such as optical and magnetic pickups. One known system employs a low output resistive strain gauge in one leg of a bridge circuit feeding a differential amplifier pair and a high gain amplifier.
Such systems are largely unattended and are exposed to all kinds of weather conditions and to industrial environments. It is thus not surprising that the sensing system must be rugged in order to avoid environmentally induced failures. Physically exposed elements of railway systems, such as the sensor itself, may well become damaged through normal wear and tear and may be rendered inoperative by virtue of adverse weather conditions acting upon the exposed equipment. In particular electrical components are particularly sensitive to adverse environmental conditions and may also be affected by electrical or magnetic interference. Overhead power lines or those adjacent to track, or high voltage sources giving rise to electrical and magnetic disturbances are often encountered. In addition weather related magnetic interference such as lightning induced surges may also affect system performance.
Some of the known systems attempt to obviate the problems outlined above. Previous efforts required welding or permanently attaching the gage to the rail. Such arrangements are impractical because they are too costly to implement.
The known system employing a low output (gage factor) resistive strain gauge required a fairly high gain amplifier, in the order of 85 db, to unambiguously detect a train wheel. Unfortunately, such high gain amplifiers are especially susceptible to noise or electromagnetic interference (EMI) and may therefore produce a false alarm. In order to assure a positive detection a high gain amplifier is required, because the transducer may experience only a small deflection. This translates into a small change in resistance resulting in a relatively small input signal. This is especially true in light rail applications particularly those using concrete ties and in mining operations where the cars are empty. In the described arrangement, the resistive strain gauge is mounted onto a uniform thickness bar which experiences uniform deflection with passing load. It is thus difficult to sense a stress induced signal.
Added difficulties arise because conventional systems require on site adjustment or calibration during set up to provide the requisite sensitivity for proper detection. This results in the need for skilled personnel to effect the initial installation and sensitivity adjustments and to effect subsequent adjustments as may be needed.